The present invention relates to a method of and an apparatus for soldering electronic devices such as ICs, LSIs, and the like, and other works using a soldering iron in a gas atmosphere.
When electronic devices and the like are soldered using a soldering iron, there has been employed a method of performing soldering while injecting an inert gas such as a nitrogen gas of high concentration (at least 99%) to a subject to be soldered. According to this method, soldering of good quality can be performed because the oxidation of solder and the subject is prevented by the inert gas as well as the wettability of a soldering iron tip and the subject to the solder is improved.
In contrast, when it is possible to use a reducing gas such as a hydrogen gas in soldering, soldering of very high quality, which cannot be realized by a conventional method, can be performed. This is because that the soldering can be performed while reducing oxide films formed to the soldering iron tip and the subject by the strong reducing action of the reducing gas.
However, the reducing gas such as the hydrogen gas and the like has not been practically used in soldering in which a soldering iron is used because it is very dangerous and difficult to use the reducing gas due to its explosive reaction with oxygen.
Accordingly, it is a technical subject of the present invention to perform soldering of high quality safely and reliably by using a reducing gas when the soldering is carried out using a soldering iron in a gas atmosphere.
To solve the above problem, according to the present invention, there is provided a gas injection type soldering method which is characterized in that after a reducing gas and an inert gas, which are supplied from gas supply sources separately, are mixed at a predetermined ratio by a mixer, a resultant mixed gas is made to a hot mixed gas by being heated by a heater so that the temperature of the mixed gas is increased and the mixed gas is dried by being dehumidified, the hot mixed gas is injected from an injection port formed in a soldering iron to a subject, and soldering is performed in the atmosphere of the mixed gas while preventing the oxidation of the subject by the inert gas in the mixed gas as well as reducing an oxide film by the reducing gas.
According to the present invention, the reducing gas and the inert gas are injected in a uniformly mixed state, and soldering is performed in the atmosphere of the mixed gas. Since soldering can be performed by reducing an oxide film by the reducing gas while preventing the oxidation of the subject by perfectly shutting off it from oxygen in outside air by the inert gas, very stable soldering of high quality can be performed. Moreover, since no flux is needed, it is not necessary to use expensive thread solder in which flux is sealed and less expensive fluxless solder can be used as well as a job for cleaning remaining flux is not necessary, from which a large economical effect can be obtained. Further, since wettability to lead-free solder containing no lead component is enhanced, it is possible to perform soldering of higher quality using the lead free solder.
Further, even if the mixed gas is injected into outside air from the soldering iron, the reducing gas does not cause an explosive reaction and is safe because the purity of the reducing gas is suppressed to a low level by being mixed with the inert gas as well as the reaction of the reducing gas is suppressed by the inert gas around it and the reducing gas reacts only with the oxide film.
In the present invention, the hot mixed can be injected simultaneously also from a solder guide for feeding thread solder to the soldering iron.
In the present invention, it is preferable that the reducing gas be a hydrogen gas, the inert gas be a nitrogen gas, and the ratio of the hydrogen gas in the mixed gas be 2 to 15%.
According to the present invention for embodying the above method, there is provided a soldering apparatus including a gas injection mechanism for injecting a mixed gas in which a reducing gas is mixed with an inert gas from an injection port to a subject and a soldering iron for performing soldering by heating and melting solder.
The gas injection mechanism includes flow regulators for individually regulating the flow rates of the reducing gas and the inert gas supplied from gas supply sources separately, a gas mixer for uniformly mixing the reducing gas and the inert gas supplied from the flow regulators, a gas heater for heating a mixed gas supplied from the gas mixer so as to dehumidify and dry it and to increase the temperature of the mixed gas, the injection port for injecting the heated hot mixed gas, and a controller capable of regulating the mixing ratio of the reducing gas and the inert gas by controlling the respective flow regulators.
In the present invention, the gas injection mechanism may further include a concentration sensor for measuring the concentration of the gas in the vicinity of the subject and a safety circuit for restricting the supply of at least the reducing gas, when the value of concentration measured by the concentration sensor exceeds a set value, by controlling the flow regulators by the controller. With this arrangement, the diffusing state of the reducing gas in the vicinity of the apparatus can be checked so that countermeasures for safety can be taken before the concentration of the reducing gas reaches a dangerous concentration.
According to a specific embodiment of the present invention, the soldering iron is a contact type soldering iron and includes a soldering iron tip at the extreme end thereof to heat and melt solder as well as the injection port opened so as to surround the soldering iron tip.
According to another specific embodiment of the present invention, the soldering iron is a non-contact type soldering iron and has the injection port at the extreme end of the soldering iron, and soldering is performed by heating and melting solder by the heat of the mixed gas itself injected from the injection port in the atmosphere of the mixed gas.
According to still another specific embodiment of the present invention, the soldering iron is a laser type soldering iron and has the injection port at the extreme end of the soldering iron, and soldering is performed by heating and melting solder by the heat of the mixed gas itself injected from the injection port in the atmosphere of the mixed gas.